1. Field of the Invention
The invention relates to a semiconductor device having metal gate and manufacturing method thereof, and more particularly, to a semiconductor device having metal gate and manufacturing method integrated with epitaxy technique.
2. Description of the Prior Art
With semiconductor processes entering the era of the deep submicron meter, it has been more and more important to increase the metal-oxide semiconductor (MOS) drive current. To improve device performance, epitaxy technique is developed to enhance carrier mobility of the channel region.
On the other hands, with the trend toward scaling down the size of the semiconductor device, work function metals are provided to replace the conventional polysilicon gate to be the control electrode that competent to the high dielectric constant (herein after abbreviated as high-K) gate dielectric layer. The metal gate methods in the-state-of-art are categorized into the gate first process and the gate last process. Among the two main processes, the gate last process is able to avoid processes of high thermal budget and to provide wider material choices for the high-K gate dielectric layer and the metal gate, and thus the gate last process gradually replaces the gate first process.
It is observed that processes with high thermal budget impacts not only the metal gate process, but also the quality of the epitaxial layers. In the view of the above, there exists a need for integrating the epitaxy technique and metal gate process without encountering the high thermal budget issue.